The purpose of this proposal is to determine the aggregation mechanism of bovine alpha-crystallin and human lens proteins and thereby to gain insight into the opacification of cataractous lenses. One feasible approach to delineating the interactions of lens protein subunits is through the chemical modification of bovine lens alpha-crystallin. The isolation and characterization of the modified alpha-crystallin aggregates of various size distributions can eventually lead to an understanding of the functional involvement of the various amino acid residues in the protein polypeptides. In addition chemical modification provides a unique opportunity to elucidate the quarternary interactions of the lens protein aggregates independent of the detailed knowledge on the crystal structure of individual lens protein. These results will also provide insight for investigating the interaction of other minor components with lens proteins, implicated in the formation of giant protein aggregates during aging and the development of human senile cataracts. Derivatized lens protein aggregates will be purified and analyzed with the various chromatagraphic procedures. Polypeptide backbone conformation and size distribution of these aggregates will be studied using spectropolarimetry and the ultracentrifuge. The role of the minor non-proteinous components in controlling the size of the alpha-crystallin aggregates will also be investigated.